CG position

[Don Fry]

Welcome.

[Jonathan M]

14 hours ago, Mike downs 1 said:

Still don’t get it…….Have I wandered on to a different thread?

 

Mike, the boys are just having a bit of word-play fun (in an immature/senile sort of way, possibly fuelled with a bit of French brandy).  It all started when I pointed out that you'd not said in your opening post exactly what you'd designed, and added that for all we knew you could have designed a flying 'carrot peeler' (which is the same thing as a potato peeler) only because it was the first object that came into my head!

 

Mind you, I'm now seriously exploring the potential for a whole series of free plans in RCM&E of designs which are inspired by kitchen utensils... starting with a potato/carrot/parsnip peeler!

 

 

Please let us know whether your thrust-line changes make the desired difference.  It'll probably be a bit of trial-and-error with different thickness shims or washers, but I'd build up the shimming gradually as you don't want a sudden nose-down when the power comes on!

 

Jon

[J D 8]

         I recon that the one on the left, two of them fitted to a fuzz would make one of them rotary wing planes.?

         Yes Mike, Carrot, potato peeler just a term for funny shaped aircraft.

[leccyflyer]

On 11/11/2021 at 17:43, Mike downs 1 said:

I have designed a flying and used a cg finding app called ecalc

it gave me a cg at 3.5” from the le

at full power it climbs steeply

,when I throttle back it levels out

any suggestions greatly appreciated 

The LE on the flying wing pictured is swept forward, plus it's a flying wing, which presumably has built-in reflex. Does the software take account of these two issues or is it for more conventional set ups?

 

Sounds like it might be a thrustline issue.

Edited November 14, 2021 by leccyflyer

[Mike downs 1]

7 hours ago, leccyflyer said:

The LE on the flying wing pictured is swept forward, plus it's a flying wing, which presumably has built-in reflex. Does the software take account of these two issues or is it for more conventional set ups?

 

Sounds like it might be a thrustline issue.

I have introduced some down thrust,but it hasn’t made that much difference,so I will try the throttle/elevator mix.

I have used the wing beds(see photo) to make a Chuck glider and have a good cg position as this glides on a good slope

that is why I will try the program mixes which has been suggested.I will report back when I get the chance to try it out. Many thanks for all the suggestions so far

[EarlyBird]

Your motor is below the wing which means adding down thrust is the traditional approach ideally the motor thrust line should go through the CofG. You can keep adding down thrust (more washers) when it dips it's nose when power is increased means you have gone too far.

 

Is there any way you could raise the motor to be in line with the wings as this would be more efficient. 

 

Keep posting as this is interesting.

[Mike downs 1]

Do you mean the thrust centre line, rather than the CG? That might be an idea to try….thanks

[Peter Jenkins]

Centre of drag rather than CG is the issue.

[J D 8]

 As noted before that is a large fin sticking up well above the thrust line.

[EarlyBird]

? 

10 hours ago, Peter Jenkins said:

Centre of drag

?

The wings and fin cause the drag and the motor creates the thrust the photo of the side elevation shows the motor below the wings, clearly showing the reason for your issue, in flight the wings are pushing back and the motor pulling forward making the nose pitch up. Judging by the size of the fin the ideal location to minimise this is for the motor to be slightly above the wing then a small adjustment of the down thrust will have a large effect. CofG comes into my logic as in flight the model rotates around this point so with the motor thrust line passing through the CofG there will be no rotational effect. I know it's just my logic but it's an approach that has put me on the right path to curing this issue. Once the thrust line is close to ideal moving the CofG can be used to fine tune. 

[Mike downs 1]

I put 3mm washers to create down thrust,I think I will add a few more.

Could it be that the motor/prop set up is too powerful, as it flies better at just over a quarter throttle.

I am getting more used to flying this model, but of I whack open the throttle it goes up like a homesick angel.

[Peter Jenkins]

How many watts per pound does your wing have Mark?

[Mike downs 1]

Sorted out the problem by making a scale Chuck glider out of depron, scaling at 1” to 1 cms. Tried that until I had a nice glide.

meant that I had to move the CG position by approx 1in h forward. Model now flies stable and slow..Picture shows both together.

many thanks to all who put forward suggestions.